A 58-year-old patient referred for proteinuria was found to have myoglobin nephropathy caused by paraneoplastic dermatomyositis secondary to smouldering multiple myeloma, highlighting the importance of screening for plasma cell dyscrasias in dermatomyositis work-up.
Key Findings
Results
Dermatomyositis can present as a paraneoplastic phenomenon secondary to smouldering multiple myeloma, an uncommon association with plasma cell dyscrasias.
The patient was a 58-year-old mixed-race gentleman
DM is often associated with malignancies but 'less commonly with plasma cell dyscrasias'
Investigations for solid organ malignancies were negative, directing attention to haematological causes
Plasma cell dyscrasia screening revealed an IgA kappa monoclonal band confirmed with serum free light chain testing
Bone marrow biopsy confirmed smouldering multiple myeloma (SMM) based on revised working group diagnostic criteria
Results
Myoglobin nephropathy caused by dermatomyositis presented as sub-nephrotic proteinuria without albuminuria, representing an extrarenal cause of proteinuria.
The patient was referred for sub-nephrotic proteinuria
Additional testing showed no associated albuminuria, distinguishing the proteinuria from glomerular origin
Haematuria on urine microscopy combined with raised creatine kinase levels suggested myoglobinuria
Kidney biopsy confirmed myoglobin nephropathy
Myoglobin nephropathy is described as 'an uncommon complication of inflammatory myopathies'
Results
The patient had a 5-month history of skin changes and 1-month history of proximal muscle weakness prior to nephrology referral, reflecting delayed recognition of dermatomyositis.
Skin changes suggestive of dermatomyositis had been present for 5 months
Proximal muscle weakness had been present for 1 month
The presenting complaint to the nephrologist was sub-nephrotic proteinuria
Recognition of the DM presentation only occurred after detailed history-taking during the nephrology referral
Conclusions
Routine screening for plasma cell dyscrasias is recommended as part of dermatomyositis work-up to enable early diagnosis prior to organ damage.
The authors state: 'Routine screening for plasma cell dyscrasias is recommended as part of DM work-up to allow the diagnosis to be made early, prior to organ damage'
In this case, the SMM was identified only after DM prompted paraneoplastic investigation
The case highlights that plasma cell dyscrasias, though uncommon, should not be omitted from DM malignancy screening
What This Means
This research describes a single patient case that illustrates an unusual chain of medical findings. A 58-year-old man was sent to a kidney specialist because protein was found in his urine. Through careful history-taking, doctors discovered he had also been experiencing skin changes for five months and muscle weakness for one month — symptoms consistent with dermatomyositis, a condition involving inflammation of both skin and muscles. Further testing showed that the protein in his urine was actually myoglobin (a protein released from damaged muscle), not a sign of kidney disease itself. A kidney biopsy confirmed that the kidneys were being damaged by this myoglobin leaking from inflamed muscles.
Because dermatomyositis is sometimes triggered by an underlying cancer (called a paraneoplastic condition), doctors investigated further. Tests for solid organ cancers came back negative, but blood tests revealed an abnormal protein produced by plasma cells. A bone marrow biopsy confirmed a diagnosis of smouldering multiple myeloma — an early-stage blood cancer involving abnormal plasma cells that has not yet caused classic myeloma symptoms.
This research suggests that when a patient is diagnosed with dermatomyositis, doctors should routinely screen for plasma cell disorders such as multiple myeloma, not just solid organ cancers. Early detection of an underlying blood cancer could allow treatment before serious organ damage occurs. The case also illustrates that protein in the urine does not always mean the kidneys themselves are diseased — sometimes the cause lies elsewhere in the body, and thorough history-taking and examination remain essential diagnostic tools.
Meel S. (2026). A rare case of paraneoplastic dermatomyositis secondary to smouldering multiple myeloma referred for proteinuria.. South African medical journal = Suid-Afrikaanse tydskrif vir geneeskunde. https://doi.org/10.7196/SAMJ.2026.v116i5.3970